Acrylic adhesives provide a wide range of performance benefits. Such adhesives include acrylic polymers that are formed using solvent and solventless polymerization techniques. Although satisfactory in many respects, artisans have attempted to utilize acrylic polymers formed by emulsion polymerization, in adhesives. Emulsion polymerization offers several advantages including ability to form high molecular weight polymers at fast polymerization rates; the water phase present in emulsion polymerization is an excellent conductor of heat, and the viscosity of the reaction medium remains relatively stable and approximately that of water.
However, a number of challenges exist in attempting to incorporate polymers formed via emulsion techniques in adhesives, and particularly in high performance adhesives. These challenges include preparing a coherent adhesive film despite the particle nature of emulsion adhesives, preparing an adhesive polymer film with a defined molecular structure including regular polymer lengths between crosslink points, providing a controlled number of entanglements between precursor or pre-crosslinked polymer chains, and preventing surfactant migration to adhesive film interfaces where such surfactant can dramatically reduce adhesion performance.
Accordingly, a need exists for emulsion-based polymers that can be effectively used in adhesive formulations.